Recently, a variety of types of display devices are actively researched and developed. Among these, much attention is focused on organic electroluminescent (EL) devices. This is because organic EL devices are promising display devices capable of emitting light of high luminance under low applied voltage.
Recently, application of organic EL devices to color displays and white light sources has been actively studied. However, development on high-grade color displays and white light sources requires enhancing the characteristics (performances) of blue-, green-, and red-emitting devices.
On the other hand, as luminescent devices using a red-emitting phosphorescent material, those using a cyclic tetradentate ligand-containing platinum porphyrin complex as a light-emitting material are known by, for example, Nature 395, 151 (1998) and U.S. Pat. No. 6,303,231 B1. However, because these devices are low in maximum luminance (brightness), enhancement of the maximum luminance has been desired.
Further, there are reports on platinum porphyrin complexes containing a bipyridine-series or phenanthroline-series chain tetradentate ligand (see Chem. Eur. J., 9, No. 6, 1264 (2003), U.S. Pat. No. 6,653,654 B1 and WO 03/093283A1). However, these complexes do not compatibly satisfy both durability and luminous characteristics, such as color purity. Accordingly, improvement on these properties is desired. Also with respect to green-emitting luminescent materials and blue-emitting luminescent materials that emit in a shorter wavelength region than the aforementioned luminescent materials, there is a need for development of advanced materials that are excellent in both luminous characteristics and durability.